1. Field of the Invention
The present invention relates generally to the field of mail processing machines and more particularly to mail processing machines in which a plurality of mixed mail pieces of varying length and thickness are stored on a supply tray and are separated and fed seriatim therefrom to a path of travel which extends through a mail processing machine.
A typical mail processing machine with which the present invention is concerned comprises a series of modules, components or subassemblies which perform independent functions on the mail pieces. For example, mail is stacked in a feed tray unsealed and is fed seriatim first to a device which opens the flap of each envelope, moistens the sealing edge and then presses the flap to seal the envelope. The sealed envelope is then fed to a mailing machine which prints a postage indicia in the upper right hand corner of the envelope in known manner. Finally, the envelope is fed to a stacking device which accumulates the mail pieces in a suitable receiving tray.
Typically, mail processing machines of the type described above are capable of operating at a rather high rate of speed, usually in the order of 100 to 300 pieces of mail per minute. At this rate of movement, it is absolutely essential that the mail pieces enter the feed path of the mail processing machine only one at a time and not in overlapped relationship. If more than one mail piece enters the mail processing machine, a jam will occur, resulting in possible damage to the mail pieces or some part of the mail processing machine or both.
It is the inherent nature of friction type sheet separating devices that they are less than perfect, and occasionally a plurality of mail pieces will enter the feed path of the mail processing machine notwithstanding the presence of a separating device at the feed end of the supply of mail pieces being fed into the mail processing machine. To avoid the aforementioned undesirable consequences of this happening, one or more separating devices are inserted in the feed path in advance of the first mail processing station to assure that only one mail piece at a time reaches the processing station. This type of arrangement has proven to be very effective to the point that when two separating devices are placed in series in the feed path, the probability of a pair of mail pieces being fed into the mail processing simultaneously is virtually nil.
The most efficient type of separating device for high speed mail processing machines is the continuation of a high friction feed roller rotating in a direction such as to feed an envelope along a feed path, and a lower friction endless belt separator adjacent the feed roller which moves in a direction such that the outer surface of the belt where it is adjacent to the peripheral surface of the feed roller moves in a direction opposite to that of the peripheral surface of the feed roller. With this arrangement, the feed roller feeds a mail piece in the desired direction notwithstanding any force applied by the belt to move the mail piece in the opposite direction because the feed roller has a higher coefficient of friction with the mail piece than does the belt. However, if two mail pieces are fed to the separator device simultaneously, the belt will hold back one mail piece while he feed roller feeds the other because the surface material of the belt has a higher coefficient of friction with the mail piece than do the two mail pieces sliding together.
One major disadvantage with the above described type of mail piece separating device is that the most satisfactory type of belts have an excessively high rate of wear. In fact, it is not uncommon for an operator of a typical mail processing machine to have to change separating belts with sufficient frequency that in an installation having several mail processing machines, each with several separating belts, belt replacement becomes a significant problem. Ordinarily, a small gap is maintained between the adjacent surfaces of the feed roller and the belt, so that mail pieces of normal thickness can be fed through the gap without any difficulty. The belt is mounted in such a way that it is movable toward and away from the feed roller in order to accommodate either thick or plural mail pieces, the former being fed past the separator belt and the latter being separated as described above. However, the mechanism on which the belt is mounted is limited to a specific amount of movement regardless of the thickness of the belt. What happens as the belt wears is that the gap between the belt surface and the roller surface gradually widens to the point where there is insufficient friction between the belt and a mail piece to assure proper separation of plural mail pieces, with the result that the mail pieces are simultaneously fed into the mail processing machine.
2. The Prior Art
The prior art is replete with various types of separating devices for a large variety of items such as sheets of various materials, mail pieces and various flat articles. Three U.S Pat. Nos. 3,373,685, 3,773,317 and 3,970,298 are typical examples of different types of combination roller and belt separating devices, although in these patents a belt functions as the feeding device and a roller functions as the separating device. No prior art is presently known which addresses the problem of belt wear in a combination roller-belt separating device where the roller is the feeding element and the belt is the separating element.
Another U.S. Pat. No. 2,140,171 issued to Francis J. Rouan, assignee to Pitney Bowes Inc., discloses a Feed and Separator Roller Wear Compensator for a mail handling machine. There is a compensating means disclosed which adjusts itself according to wear upon a feed roller and an adjacent separator roller. However, the apparatus disclosed depends for its operation on plural compensating devices acting simultaneously on adjacent feed and separator rollers to maintain a predetermined minimum gap therebetween, and therefore is very complex in construction and difficult to maintain in operation.